River Crossing Problem

Mind Teasers :
River Crossing Problem

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A guard is positioned at the one side of bridge say 'A'.
* His task is to shoot all those who try to leave from 'A' to other side say 'B'.
* He also need to welcome the person who come from other side 'B' to his side 'A'.

The guard comes out of his post every 1 hour and looks down the bridge for any people trying to leave.
Monica a brilliant girl is at side 'A' and wish to go to other side 'B'. She also know's it would take her 1:45 hr to cross the river.

She comes with an super idea and able to cross the river.How did Monica cross the river ?

Steps
1. Monica go from side A to B for approx 59 minutes
2. Lisa then move back to side A for 2 minutes to fool guard. Now guard will think she is coming to side A.
3. then she again move toward B :-)

A clever robber breaks into a closed bank where he finds a clerk. He asks password of the safe from the clerk while pointing a gun on his forehead. Out of fear, the clerk manages to blurt out, “Every day, the password of the safe is changed. I can help you but please point away the gun as if you kill me, you will never be able to crack the password.

The robber ties the clerk on a chair and insert a cloth in his mouth. He then easily opens the safe after inserting the code and takes all the money before he flees.

On a random day , i was not able to logged-in with my bank password , so i contacted them on phone.
Our conversation is stated as :

myself : My password is altered.
myself : I am not able to logged-in.
customer-executive : Your password is distinct this time and it got 8 letters , out of which 2 are same of your previous password.
myself: Thanks , now i am able to logged-in.

100 people are standing in a circle. The person standing at number 1 is having a sword. He kills the person next to him with the sword and then gives the sword to the third person. This process is carried out till there is just one person left.

Explanation:
Till the number is the power of 2, the last person to survive will be the one who started it. But since the number here is not the power of 2, we will take the greatest power of 2 that is less than the number which is 64.
100 - 64 = 36
36 people are killed as 2, 4, 6, ..., 72. Thus the sword will now be given to the 73rd person. Now he is the first person to start in the remaining 64 people. Thus he will be the one to survive.

A square island comprised of a square castle. A 14m wide trench surrounded the island from everywhere. Roman Empire wanted to invade the castle and gain the loot as well as possession of the island. They brought along wooden planks to cross the trench. However, they realized that the planks were just 13m long.

How did they use those planks to invade as well as capture the island ?

A girl liked to collect money in a piggy bank. She bought pink colored piggy bank when she was 10 years old. She put $250 in the box on each of her birthday. Her younger sister took $50 out of her piggy bank on her birthday. The girl died when she was 50 years old due to an incurable disease.

When the piggy bank was opened, it had just $500. How can that be possible?

The girl was born on 29 February. Thus her birthday came once in four years only while her sister was born on a normal day and celebrated her birthday every year. Thus the girl had a chance of depositing money only 10 times in 4 years through which she collected $2500 while her sister took $50 from the piggy bank every year making the total amount to be $2000. Thus when the piggy bank was opened, it had just $500.